Tendon repair implant and method of arthroscopic implantation

ABSTRACT

A tendon repair implant for treatment of a partial thickness tear in the supraspinatus tendon of the shoulder is provided. The implant may incorporate features of rapid deployment and fixation by arthroscopic means that compliment current procedures; tensile properties that result in desired sharing of anatomical load between the implant and native tendon during rehabilitation; selected porosity and longitudinal pathways for tissue in-growth; sufficient cyclic straining of the implant in the longitudinal direction to promote remodeling of new tissue to tendon-like tissue; and, may include a bioresorbable construction to provide transfer of additional load to new tendon-like tissue and native tendon over time.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/046,624 filed on Mar. 11, 2011, entitled “TENDON REPAIR IMPLANT ANDMETHOD OF ARTHROSCOPIC IMPLANTATION”, which claims benefit to U.S.Provisional Patent Application No. 61/313,113, entitled, “TENDON REPAIRIMPLANT AND METHOD OF ARTHROSCOPIC IMPLANTATION” filed on Mar. 11, 2010.The disclosures of each of which are herein incorporated by reference intheir entirety.

INCORPORATION BY REFERENCE

This present application is related to: U.S. patent application Ser. No.12/684,774, filed Jan. 8, 2010; U.S. patent application Ser. No.12/729,029, filed Mar. 22, 2010; U.S. patent application Ser. No.12/794,540, filed Jun. 4, 2010; U.S. patent application Ser. No.12/794,551, filed Jun. 4, 2010; U.S. patent application Ser. No.12/794,673, filed Jun. 4, 2010; U.S. patent application Ser. No.12/794,677, filed Jun. 4, 2010; U.S. Provisional Patent Application No.61/443,180, filed Feb. 15, 2011; U.S. Provisional Patent Application No.61/443,169, filed Feb. 15, 2011, all of which are incorporated herein byreference. All publications and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication or patent application was specificallyand individually indicated to be incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to orthopedic implants andmethods of treatment. More particularly, the present invention relatesto a tendon repair implant, such as one that is engineered forarthroscopic placement over or in the area of a partial thickness tearin the supraspinatus tendon of the shoulder.

BACKGROUND OF THE INVENTION

As disclosed by Ball et al. in U.S. Patent Publication No. US2008/0188936 A1 and illustrated in FIG. 1, the rotator cuff 10 is thecomplex of four muscles that arise from the scapula 12 and whose tendonsblend in with the subjacent capsule as they attach to the tuberositiesof the humerus 14. The subscapularis 16 arises from the anterior aspectof the scapula 12 and attaches over much of the lesser tuberosity. Thesupraspinatus muscle 18 arises from the supraspinatus fossa of theposterior scapula, passes beneath the acromion and the acromioclavicularjoint, and attaches to the superior aspect of the greater tuberosity 11.The infraspinatus muscle 13 arises from the infraspinous fossa of theposterior scapula and attaches to the posterolateral aspect of thegreater tuberosity 11. The teres minor 15 arises from the lower lateralaspect of the scapula 12 and attaches to the lower aspect of the greatertuberosity 11. Proper functioning of the rotator depends on thefundamental centering and stabilizing role of the humeral head 15 withrespect to sliding action during anterior and lateral lifting androtation movements of the arm.

The insertion of these tendons as a continuous cuff 10 around thehumeral head 17 permits the cuff muscles to provide an infinite varietyof moments to rotate the humerus 14 and to oppose unwanted components ofthe deltoid and pectoralis muscle forces. The insertion of theinfraspinatus 13 overlaps that of the supraspinatus 18 to some extent.Each of the other tendons 16, 15 also interlaces its fibers to someextent with its neighbor's tendons. The tendons splay out andinterdigitate to form a common continuous insertion on the humerus 14.

The rotator cuff muscles 10 are critical elements of this shouldermuscle balance equation. The human shoulder has no fixed axis. In aspecified position, activation of a muscle creates a unique set ofrotational moments. For example, the anterior deltoid can exert momentsin forward elevation, internal rotation, and cross-body movement. Ifforward elevation is to occur without rotation, the cross-body andinternal rotation moments of this muscle must be neutralized by othermuscles, such as the posterior deltoid and infraspinatus. The timing andmagnitude of these balancing muscle effects must be preciselycoordinated to avoid unwanted directions of humeral motion. Thus thesimplified view of muscles as isolated motors, or as members of forcecouples must give way to an understanding that all shoulder musclesfunction together in a precisely coordinated way—opposing musclescanceling out undesired elements leaving only the net torque necessaryto produce the desired action. Injury to any of these soft tissues cangreatly inhibit ranges and types of motion of the arm.

The mechanics of the rotator cuff 10 are complex. The cuff muscles 10rotate the humerus 14 with respect to the scapula 12, compress thehumeral head 17 into the glenoid fossa providing a critical stabilizingmechanism to the shoulder (known as concavity compression), and providemuscular balance. The supraspinatus and infraspinatus provide 45 percentof abduction and 90 percent of external rotation strength. Thesupraspinatus and deltoid muscles are equally responsible for producingtorque about the shoulder joint in the functional planes of motion.

With its complexity, range of motion and extensive use, a fairly commonsoft tissue injury is damage to the rotator cuff or rotator cufftendons. Damage to the rotator cuff is a potentially serious medicalcondition that may occur during hyperextension, from an acute traumatictear or from overuse of the joint. With its critical role in abduction,rotational strength and torque production, the most common injuryassociated with the rotator cuff region is a strain or tear involvingthe supraspinatus tendon. A tear in the supraspinitus tendon 19 isschematically depicted in FIG. 2. A tear at the insertion site of thetendon with the humerus, may result in the detachment of the tendon fromthe bone. This detachment may be partial or full, depending upon theseverity of the injury. Additionally, the strain or tear can occurwithin the tendon itself. Injuries to the supraspinatus tendon 19 andrecognized modalities for treatment are defined by the type and degreeof tear. The first type of tear is a full thickness tear as alsodepicted in FIG. 2, which as the term indicates is a tear that extendsthrough the thickness of the supraspinatus tendon regardless of whetherit is completely torn laterally. The second type of tear is a partialthickness tear which is further classified based on how much of thethickness is torn, whether it is greater or less than 50% of thethickness.

The accepted treatment for a full thickness tear or a partial thicknesstear greater than 50% includes reconnecting the torn tendon via sutures.For the partial thickness tears greater than 50%, the tear is completedto a full thickness tear by cutting the tendon prior to reconnection. Intreating a full thickness tear or partial thickness tear of greater than50% after completing the tear by cutting the tendon, accepted practicealso can include the placement of scaffolds and patches over therepaired tendon to shield the sutured or repaired tendon area fromanatomical load during rehabilitation. For example, Wright Medicaldisclose that the GraftJacket® can be used to augment a suture repairedtendon in large and massive full-thickness tears or smallerfull-thickness tears in a shoulder having severely degenerated tissue.However, it is recognized that significant shielding of the tendon fromload can lead to atrophy and degeneration of the native tendon andmuscle.

It is known that, for the rotator cuff, allowing the tendon toexperience full anatomical load during recovery after repairing thetendon tear with sutures will result in a 20-60% failure rate. Ball etal. (US Patent Appl. No. 2008/0188936 A1) disclose an implant thatprovides a healing modality that shields the tendon from most of theanatomical loads in the early part of the recovery period, and graduallyexperience increasing loads as the repair heals to full strength. Ballet al. disclose the strength of the surgical repair, expressed aspercent strength of the final healed repair, begins post-surgically atthe strength of the suture-to-tissue connection alone. In theirillustrated example, the suture-to-tissue connection represents about25% of the strength. The augmentation implant initially receives the 75%of the loads experienced during recovery through high initial strength.Gradually, the ratio of load sharing shifts to the suture-to-tissueconnection as the repair heals and gains strength, while the implant issimultaneously absorbed by the body. Strength retention is defined torefer to the amount of strength that a material maintains over a periodof time following implantation into a human or animal. For example, ifthe tensile strength of an absorbable mesh or fiber decreases by halfover three months when implanted into an animal or human, the mesh orfiber's strength retention at 3 months would be 50%.

In contrast to the treatment of a full thickness tear or a partialthickness tear of greater than 50%, the treatment for a partialthickness tear less than 50% usually involves physical cessation fromuse of the tendon, i.e., rest. Specific exercises can also be prescribedto strengthen and loosen the shoulder area. In many instances, theshoulder does not heal and the partial thickness tear can be the sourceof chronic pain and stiffness. Further, the pain and stiffness may causerestricted use of the limb which tends to result in further degenerationor atrophy in the shoulder. Surgical intervention may be required for apartial thickness tear of less than 50%. However, current treatmentinterventions do not include repair of the tendon. Rather, the surgicalprocedure is directed to arthroscopic removal of bone to relieve pointsof impingement or create a larger tunnel between the tendon and bonethat is believed to be causing tendon damage. As part of the treatment,degenerated tendon may also be removed using a debridement procedure.Again, the tendon partial tear is not repaired. Several authors havereported satisfactory early post operative results from theseprocedures, but over time recurrent symptoms have been noted. In theevent of recurrent symptoms, many times a patient will “live with thepain”. This may result in less use of the arm and shoulder which furthercauses degeneration of the tendon and may lead to more extensive damage.A tendon repair would then need to be done in a later procedure if theprescribed treatment for partial tear was unsuccessful in relieving painand stiffness or over time the tear propagated through injury ordegeneration to a full thickness tear or a partial thickness teargreater than 50% with attendant pain and debilitation. A subsequentlater procedure would include the more drastic procedure of completingthe tear to full thickness and suturing the ends of the tendon backtogether. This procedure requires extensive rehabilitation, hasrelatively high failure rates and subjects the patient who firstpresented and was treated with a partial thickness tear less than 50% toa second surgical procedure.

As described above, adequate treatments do not currently exist forrepairing a partial thickness tear of less than 50% in the supraspinatustendon. Current procedures attempt to alleviate impingement or make roomfor movement of the tendon to prevent further damage and relievediscomfort but do not repair or strengthen the tendon. Use of the stilldamaged tendon can lead to further damage or injury. Prior damage mayresult in degeneration that requires a second more drastic procedure torepair the tendon. Further, if the prior procedure was only partiallysuccessful in relieving pain and discomfort, a response may be to usethe shoulder less which leads to degeneration and increased likelihoodof further injury along with the need for more drastic surgery. There isa large need for surgical techniques and systems to treat partialthickness tears of less than 50% and prevent future tendon damage bystrengthening or repairing the native tendon having the partialthickness tear.

SUMMARY OF THE INVENTION

In accordance with aspects of the disclosure, a tendon repair implant isprovided that can be relatively quickly implanted during an arthroscopicprocedure to treat symptoms related to a partial thickness tear, such asin the supraspinatus tendon of the shoulder. With current treatmentmodalities, a partial thickness tear is treated without repair of thetendon itself, but rather procedures are directed to removing bone thatmay be impinging upon or restricting movement of the tendon. Othercurrent procedures may include debridement of degenerated tendon, butagain nothing is done to repair the tendon.

In some embodiments, the tendon repair implant can include a sheet-likestructure having desired properties and format for repairing the partialthickness tear. In particular, the sheet-like structure may beconstructed to have a first compact configuration for delivery from anarthroscopic instrument and a second planar configuration defined by alongitudinal, lateral and thickness dimension with a longitudinalsurface generally conformable to a bursal side surface of thesupraspinatus tendon when positioned thereon. The sheet-like structuremay have a tensile modulus of about 5 MPa to about 100 MPa in the rangeof 1% to 3% strain in the longitudinal dimension and a porosity of about30% to about 90%. Further the sheet-like structure may includelongitudinal pathways defined in the thickness dimension for at leastsome tissue in-growth oriented in the longitudinal dimension. Theoriented tissue in-growth coupled with cyclic straining and load sharingwith the implant result in remodeling of new tissue in-growth to formoriented tendon-like tissue that strengthens the native tendon.

In some embodiments, the physical properties of the sheet-like structureresult in load sharing between native tendon and the tendon repairimplant immediately following surgery. In some embodiments, about 1% toabout 50% of the load on the combination of native tendon and implant iscarried by the implant. In some embodiments, about 5% to about 33% ofthe load is carried by the implant or sheet-like structure. Further, thesheet-like structure may be manufactured from a bioabsorbable orbioresorbable material so that over time the implant degrades and moreof the load on the implant/native tendon combination is transferred tonew tissue in-growth in the implant along with the native tendon.

The detailed disclosure also includes a method of treating a partialthickness tear in the supraspinatus tendon of the shoulder. The methodincludes providing a sheet-like structure having a first compactconfiguration for delivery from an arthroscopic instrument and a secondplanar configuration defined by a longitudinal, lateral and thicknessdimension. The selected sheet-like structure may have a tensile modulusof about 1 MPa to about 100 MPa in the range of 1% to 3% strain in thelongitudinal dimension and a porosity of about 30% to about 90% withlongitudinal pathways defined in the longitudinal direction through thethickness dimension. In some embodiments, the tensile modulus is about 5MPa to about 50 MPa in the range of 1% to 3% strain in the longitudinaldirection. The shoulder may be arthroscopically accessed, in particularthe bursal side surface of the supraspinatus tendon with the sheet-likestructure in the first configuration. The sheet-like structure may thenbe deployed, transforming to the second planar configuration wherein aplanar surface of the sheet-like structure extends over the partialthickness tear and is in contact with and generally conforms to thebursal surface of the tendon with the longitudinal dimension extendingin the lengthwise direction of the tendon. The sheet-like structure maythen be affixed to the tendon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified perspective view of the human rotator cuff andassociated anatomical structure;

FIG. 2 is a schematic depiction of a full thickness tear in thesupraspinatus tendon of the rotator cuff of FIG. 1;

FIG. 3 is an anterior view showing the upper torso of a patient with theleft shoulder shown in cross-section.

FIG. 4 is an enlarged, cross-sectional view showing the left shoulderdepicted in FIG. 3.

FIG. 5 is an enlarged schematic cross-sectional view of a shouldershowing partial thickness tears and an exemplary tendon repair implantpositioned thereon;

FIG. 6 is a schematic representation of the load sharing between thesupraspinatus tendon and an exemplary tendon repair implant positionedand affixed thereon;

FIG. 7 is a magnified image of an exemplary tendon repair implantincluding a sheet-like structure having a woven strand and multifilamentconfiguration;

FIG. 8 is a magnified image of a cross section of the implant of FIG. 7;

FIG. 9 is a representation of another exemplary tendon repair implantincluding a sheet-like structure having multiple layers of amicromachined polymer material;

FIG. 10 schematically depicts the pattern of material removed from thestructure of FIG. 9 illustrating the longitudinal pathways createdthrough the structure;

FIG. 11 is a magnified image of another exemplary tendon repair implantincluding a sheet-like structure having an array of nanofibers formingthe structure;

FIG. 12 is a magnified image of another exemplary tendon repair implantincluding a sheet-like structure formed from a synthetic spongematerial; and

FIG. 13 is a magnified image of another exemplary tendon repair implantincluding a sheet-like structure formed from a reconstituted collagenmaterial.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description should be read with reference to thedrawings in which similar elements in different drawings are numberedthe same. The drawings, which are not necessarily to scale, depictillustrative embodiments and are not intended to limit the scope of theinvention.

FIG. 3 is a stylized anterior view of a patient 28. For purposes ofillustration, a shoulder 26 of patient 28 is shown in cross-section inFIG. 3. Shoulder 26 includes a humerus 24 and a scapula 23. The movementof humerus 24 relative to scapula 23 is controlled by the muscles of therotator cuff as previously discussed with respect to FIG. 1. Forpurposes of illustration, only the supraspinatus 30 is shown in FIG. 3.With reference to FIG. 3, it will be appreciated that a distal tendon 22of the supraspinatus 30 (hereinafter referred to as the supraspinatustendon) meets humerus 24 at an insertion point 32.

FIG. 4 is an enlarged cross sectional view of shoulder 26 shown in theprevious figure. In FIG. 4, a head 36 of humerus 24 is shown mating witha glenoid fossa of scapula 23 at a glenohumeral joint 38. The glenoidfossa comprises a shallow depression in scapula 23. A supraspinatus 30and a deltoid 34 are also shown in FIG. 4. These muscles (along withothers) control the movement of humerus 24 relative to scapula 23.

A distal tendon 22 of supraspinatus 30 meets humerus 24 at an insertionpoint 32. In the embodiment of FIG. 4, tendon 22 includes a damagedportion 140 located near insertion point 32. Damaged portion 40 includesa tear 42 extending partially through tendon 22. Tear 42 may be referredto as a partial thickness tear. The depicted partial thickness tear ison the bursal side of the tendon; however, the tear can be on theopposite or articular side of the tendon or may include internal tearsto the tendon not visible on either surface. Tendon 22 of FIG. 4 hasbecome frayed. A number of loose tendon fibers 44 are visible in FIG. 4.

Scapula 23 includes an acromium 21. In FIG. 4, a subacromial bursa 20 isshown extending between acromium 21 of scapula 23 and head 36 of humerus24. In FIG. 4, subacromial bursa 20 is shown overlaying supraspinatus30. Subacromial bursa 20 is one of more than 150 bursae found the humanbody. Each bursa comprises a fluid filled sac. The presence of thesebursae in the body reduces friction between bodily tissues.

FIG. 5 is an additional cross sectional view of shoulder 26 shown in theprevious figure. In the embodiment of FIG. 5, a tendon repair implant 25has been placed over the partial thickness tear 42. In this embodiment,the tendon repair implant 25 is placed on the bursal side of the tendonregardless of whether the tear is on the bursal side, articular side orwithin the tendon. Further, the tendon repair implant may overlaymultiple tears, as also shown in FIG. 5.

In some embodiments, the tendon repair implant is engineered to providea combination of structural features, properties and functions that areparticularly appropriate for treating a partial thickness tear of lessthan 50% without physically cutting, then suturing the tendon, as isdone in treating full thickness tears or partial thickness tears greaterthan 50%. These features may include: rapid deployment and fixation byarthroscopic means that compliment current procedures; tensileproperties that result in desired sharing of anatomical load between theimplant and native tendon during rehabilitation; selected porosity andlongitudinal pathways for tissue in-growth; sufficient cyclic strainingof the implant, having new tissue in-growth, in the longitudinaldirection to promote remodeling of new tissue to tendon-like tissue;and, the tendon repair implant is bioresorbable or otherwise absorbableto provide transfer of additional load to native tendon over time.

In some embodiments, tendon repair implants are structured for rapiddeployment and fixation by arthroscopic means to compliment currenttechniques used to relieve impingement or restricted movement of tendonrelative to bone, such as acromioplasty and tunneling procedures inpartial thickness tear treatments. The tendon repair implant 25 is agenerally sheet-like structure that has a surface that conforms to thetendon surface when implanted. Further, the physical properties of theimplant may be such that no significant pre-stretching or pre-loading ofthe implant during placement is required for it to function in sharing asufficient portion of the anatomical load with the native tendon, asdiscussed below. Stated another way, the tensile properties of theimplant may be designed to share a sufficient portion of the anatomicalload present during rehabilitation by laying the implant in surface tosurface contact with the tendon without any significant wrinkles.Therefore, the tendon repair implant may be delivered in a folded,rolled or other reduced configuration through an arthroscopic instrumentand spread out into the sheet-like shape with its surface in contact andgenerally conforming to the tendon surface without significantstretching before fixation to the tendon. Fixation may be accomplishedvia arthroscopic suturing or stapling techniques.

The sheet-like structure is defined by a longitudinal dimension, alateral dimension and a thickness. In some embodiments, lateral andlongitudinal dimensions of the implant may range from about 14 mm. to 24mm. in the lateral direction and 20 mm. to 32 mm. in the longitudinaldirection. The thickness of the sheet-like structure may be about 0.5mm. to 2.5 mm. Upon implantation, the longitudinal dimension may extendgenerally in or parallel to the load bearing direction of the tendon. Asdepicted in the embodiment shown in FIG. 5, the longitudinal directionfollows the supraspinatus tendon from its origin in the supraspinatusmuscle down to the area of attachment on the humerus. As is wellunderstood in the art, loading of the tendon is in this generaldirection upon contraction of the supraspinatus muscle.

Current procedures for repairing full thickness tears or partialthickness tears greater than 50% include cutting and suturing of thetendon itself and may include the addition of an implant that isdesigned to shield the tendon repair area from experiencing stressesduring use. With current stress shielding implants the concern is thestrain and load at which the implant versus the suture repair fails, asthe goal is to prevent suture failure during excessive loading. Incontrast, the tendon repair implants in some embodiments of the presentdisclosure have tensile properties to selectively share the anatomicalload between damaged native tendon and the implant during the normalrange of strains experienced during rehabilitation.

The tensile properties of some tendon repair implants described in thepresent disclosure for partial thickness tears less than 50% areengineered to selectively share the anatomical load duringrehabilitation. The strain and loads experienced by the both the nativetendon and affixed implant during use are explained with respect to theschematic diagram of FIG. 6. As installed over the damaged tendon, thetendon repair implant 25 and native tendon 22 are two generally parallelstructures that each carry a portion of a load 27 generated bycontraction of the supraspinatus muscle 30. The relative load carried byeach depends on the tensile properties of the each structure. Asparallel structures, the tendon repair implant 25 and the native tendon22 each experience the same strain under a given load. It is known thatnative tendon will fail at strains of about 8%, and in normal usetendons experience less than 5% strain. In rehabilitation after surgery,the native tendon is exposed to strains of about 0% to 3%. In someembodiments, tendon repair implants of the present disclosure areengineered with tensile properties in the range of 1% to 3% strain inorder to properly share anatomical load during rehabilitation, as thisis the range over which tensile properties affect the function of theimplant. To accomplish load sharing, the tensile modulus of the implantshould be less than the tensile modulus of the tendon which results inthe load on the implant being less than the load on the native tendon.In some embodiments, the tensile modulus of the implant ranges fromabout 1 MPa. to about 100 MPa. In some embodiments, the tensile modulusis from about 20 to about 50 MPa. in the range of 1% to 3% strain. Thevalue for a given material structure may be calculated from a best fitlinear regression for data collected over the range of 1% to 3% strain.Depending upon the particular native tendon on which the implant islocated, this may result in initial load sharing following surgery withabout 1% to about 50% being carried by the implant. In some embodiments,about 10% to about 30% may be carried by the implant. The load on thesupraspinatus tendon during rehabilitation may be about 50 N. to about100 N., translating to a load on the implant of about 10 N to about 20N. The tensile modulus can be measured with a 1 N. preload at zerostrain and elongation rate of 1% per second after positioning thesheet-like structure in a generally flat and non-wrinkled format.

In some embodiments, a tendon repair implant of the present disclosureincludes a selected porosity and longitudinal pathways for tissuein-growth. In some useful embodiments, the sheet-like structure of theimplant comprises a material defining a plurality of pores thatencourage tissue growth therein. The porosity and tissue in-growthallows for new collagen to integrate with collagen of the native tendonfor functional load carrying. A coating that encourages tissue growth orin-growth may be applied to the surfaces of the sheet-like structure. Itwill be appreciated that sheet-like structure may comprise various poredefining structures without deviating from the spirit and scope of thepresent description. In some embodiments, the sheet-like structure has apore size in the range of about 20 to about 400 microns. In someembodiments the pore size is in the range of about 100 microns to about300 microns, and in some embodiments it is about 150 to about 200microns. The porosity may be about 30% to about 90%, or it may be withinthe range of at least about 50% to about 80%. Examples of pore definingstructures are discussed in more detail below for specific embodiments,but may include, but not be limited to open cell foam structures, meshstructures, micromachined layered structures and structures comprising aplurality of fibers. In some embodiments, the fibers may be interlinkedwith one another. Various processes may be used to interlink the fiberswith one another. Examples of processes that may be suitable in someapplications include weaving, knitting, and braiding.

Tendon repair implants of the present invention may have a porositygreater than 50%, however, the porosity may be further structured toinclude tissue in-growth pathways in the longitudinal direction of theimplant. Pathways may be included to extend through the thickness of theimplant or laterally in the plane of the implant. Pathways may includesegments extending longitudinally in the plane of the implant. In someembodiments, longitudinally extending pathways comprise a majority ofthe porosity with such pathway segments having cross sections of about150 to about 200 microns. Longitudinal pathways may be open channels orlumens that extend in the longitudinal direction in the plane of thesheet-like structure when laying flat. They may be defined in thethickness of the sheet in the longitudinal direction. Further, theselongitudinal pathways may generally be maintained when the implant issubjected to longitudinal loads experienced during rehabilitation.

A tendon repair implant may include tensile properties that allow forcyclic straining of the implant and new tissue in-growth to cause andfacilitate remodeling of this new tissue to a more organized structureresembling tendon-like tissue. In some embodiments, the new tissue,based on the tensile properties of the implant, experiences tendon-likestrain during rehabilitation. The tendon-like tissue, which may not beas strong as native tendon, has added load bearing strength in thelongitudinal direction relative to unorganized tissue. This remodelingof tissue begins within 4 to 8 weeks after implant and continues formonths. The strength of the new tissue continues to increase as collagenfibers become more oriented due to the proper strain signal resultingfrom the properties of the implant. To facilitate cyclic loading, thetendon repair implant may have a compressive modulus greater than thenative tendon. A published value for the compressive modulus of thesupraspinatus tendon is in the range of 0.02-0.09 MPa (J Biomech Eng2001, 123:47-51). In some embodiments, the implant provided by theimplantable device should have a higher compressive modulus than thetendon to prevent collapse of pores in the implant. The compressivemodulus may be at least about 0.1 MPa, or at least about 0.2 MPa.

In some embodiments, the tendon repair implant is bioresorbable,biodegradable or otherwise absorbable to provide transfer of additionalload to native tendon over time. By 2-3 months after implant, the newtissue in-growth should have gained strength through remodeling and itmay be desirable to transfer more load from the implant to the newtissue and native tendon combination. Absorption of the implant enablesthe new tissue, in combination with the native tendon, to carry all ofthe load and develop optimal collagen fiber alignment. Further,absorption avoids potential long-term problems with particles fromnon-absorbable materials. The tissue within the device implant willtypically be developing and organizing during the first one to threemonths after implantation, so load sharing with the implant is desiredin some embodiments. After three months the tissue will typically beremodeling, so the mechanical properties of the implant should graduallydecline to zero to enable the new tissue to be subjected to load withoutthe implant bearing any of the load. If the implant loses modulus fasterthan it loses strength, then the relative loads on the implant will beless at three months than when first implanted. For example, if themodulus of the implant drops 50% to 25 MPa at three months, then 2%strain of the implant would require a stress of only about 0.5 MPa. Atthe same time, if the strength of the implant drops about 30% to 3.5MPa, then the strength of the implant will be about seven times theanticipated loads at three months, compared to about five times whenfirst implanted. Therefore, with the design criteria provided above,tensile failure of the implant during the first three months should beunlikely. Accordingly, the following specifications for degradation rateare recommended in some embodiments: an ultimate tensile strength of atleast 70% strength retention at three months; tensile and compressivemodulus of at least 50% strength retention at three months; and nominimum specification for strength and modulus at 6 months. The devicemay be designed to have a degradation profile such that it is at least85% degraded in less than 1 to 2 years after implantation.

Cyclic creep is another design constraint to be considered in someembodiments. A strain of about 2% with a 30 mm long implant will resultin an elongation of about only 0.6 mm. Therefore, very little cycliccreep can be tolerated in these embodiments to ensure that the implantwill undergo strain with each load cycle. A test where a proposedimplant design is cyclically strained to 2% at 0.5 Hz with rest periodsfor 8 hours provides 9000 cycles, which likely exceeds the number ofcycles experienced in three months of rehabilitation of a patient'sjoint. Incorporation of relaxation times should be considered in suchtesting. In some embodiments, a maximum of about 0.5% creep is anacceptable specification.

In some useful embodiments, the tendon repair implant comprises one ormore bioabsorbable materials. Examples of bioabsorbable materials thatmay be suitable in some applications include those in the followinglist, which is not exhaustive: polylactide, poly-L-lactide (PLLA),poly-D-lactide (PDLA), polyglycolide (PGA), polydioxanone,polycaprolactone, polygluconate, polylactic acid-polyethylene oxidecopolymers, modified cellulose, collagen, poly(hydroxybutyrate),polyanhydride, polyphosphoester; poly(amino acids), poly(alpha-hydroxyacid) or related copolymers materials.

The tendon repair implant may be configured to allow loading andretention of biologic growth factors. The implant and/or the growthfactors may be configured to controllably release the growth factors.The implant may be configured to allow transmission of body fluid toremove any degradation bi-products in conjunction with a potentialelution profile of biologics. The implant may also include platelet richplasma at the time of implant or other biologic factor to promotehealing and tissue formation.

A tendon repair implant of the present invention can include multiplelayers or surface coatings. As implanted, the bursal side of the implantcan include a layer or surface that will preferably slide against tissuewithout adherence. The tendon side of the implant may include a layer orcoating that is more compatible with fixation to the tendon surface.

Various materials and formats may be used to produce tendon repairimplants of the present invention. Each material and format isengineered to include selected material properties in the rangesdiscussed above. Material properties can be altered in the materialsmaking up the sheet like structure or by altering the format or patternof the material to adjust physical properties of the compositestructure.

One material and format for the sheet-like structure 50 is shown in FIG.7. The structure 50 is a woven material including multiple strands 52 ofa polymeric material, with each strand 52 including multiple filaments53. The strands 52 include a weave pattern that foams longitudinallyextending pathways 51 as depicted in the cross section view of FIG. 8.These longitudinally extending pathways have a cross section of about150 to about 200 microns as indicated. One material for the filaments ispoly-L-lactic acid.

An alternative material and format for the sheet-like structure 50 isshown in FIG. 9. The sheet-like structure 50 includes multiple layers 56of micro-machined sheets. The composite of layered sheets formlongitudinally extending pathways 58. This is best illustrated in FIG.10, which shows the material that is removed from the sheets, indicatingthe pathways defined in the structure. These sheets are preferably madeup of a blend of poly-L-lactic acid and polycaprolactone. Alternatively,individual sheets may be made of one or both of the polymers. The crosssection of the longitudinally extending pathways may be about 150 toabout 200 microns.

In another alternative material and format, the sheet-like structure 50of the tendon repair implant is made up of electro-spun nanofiberfilaments 60 forming a composite sheet. An SEM of the compositestructure is depicted in FIG. 11. The filaments have a cross section ofabout 5 microns. The filaments can be formed in a random pattern or canbe aligned to alter the mechanical properties of the composite andcreate longitudinally extending pathways for tissue migration. Thefilaments may be made up of a blend of poly-L-lactic acid andpolycaprolactone.

Another alternative material and format for the sheet-like structure 50can include a synthetic sponge material as depicted in FIG. 12. As theSEM photograph indicates, longitudinally extending pathways are definedthrough the open cell structure. The open pores may be between about 150to about 200 microns in cross section and may be interconnected in arandom pattern. A similar cell structure can also be found in anotheralternative material and format manufactured from reconstituted collagenand depicted in the magnified image of FIG. 13. This structure includeslongitudinal alignment of the collagen material to create longitudinalpathways 66. Physical properties of the collagen material may beadjusted through cross-linking.

According to aspects of the present detailed disclosure, methods oftreating a partial thickness tear in a tendon are also provided. In somemethods, supraspinatus tendons having partial thickness tears of lessthan 50% are treated. The treatment site may be first arthroscopicallyaccessed in the area of the damaged tendon. A tendon repair implant,such as previously described may be placed over a partial tear in atendon. In some embodiments, the implant may be placed over a tendonhaving micro-tear(s), abrasions and/or inflammation. Left untreated,minor or partial tendon tears may progress into larger or full tears.According to aspects of the present disclosure, a small or partial tearmay be treated by protecting it with a tendon repair implant asdescribed above. Such early treatment can promote healing and preventmore extensive damage from occurring to the tendon, thereby averting theneed for a more involved surgical procedure.

For arthroscopic delivery of the tendon repair implant, the implant maybe configured to be collapsible so that it may be inserted into ormounted on a tubular member for arthroscopic insertion to the treatmentsite. For example, the implant and associated delivery device may becollapsed like an umbrella where the deployed delivery systems unfoldsthe pleats of the implant as mounted thereon to allow surface to surfaceengagement with the tendon without any substantial wrinkles. Once flatagainst the tendon, the tendon repair implant may then be affixed usingsutures or other suitable means such as staples such that the tensileproperties will assure that the anatomical load will be shared becausethe native tendon and implant experience the same strain under load.

In summary, the tendon repair implant may comprise an absorbablematerial. In some embodiments, the purpose of the implant is to protectan injured portion of a tendon during healing, provide an implant fornew tissue growth, and/or temporarily share some of the tendon loads.The implant may induce additional tendon-like tissue formation, therebyadding strength and reducing pain, micro strains and inflammation. Whenthe implant is applied to a structurally intact, partially torn tendon,the initial loading of the implant may be less than that carried bynative tendon tissue until collagen is formed during the healingprocess. In some embodiments, organized collagen fibers are created thatremodel to tendon-like tissue or neo-tendon with cell vitality andvascularity. Initial stiffness of the device may be less than that ofthe native tendon so as to not overload the fixation while tendon tissueis being generated.

It is desirable in some situations to generate as much tissue aspossible within anatomical constraints. In some cases where a tendon isdegenerated or partially torn, tendon loads are relatively low duringearly weeks of rehabilitation. For example, the load may be about 100 N.The strain in the tendon due to the load during rehabilitation can beabout 2%. In some of these cases, the tendon repair implant can bedesigned to have an ultimate tensile strength of at least about 2 MPa.The tensile modulus may be designed to be no more than about 50 MPa andno less than about 5 MPa. The compressive modulus may be designed to beat least about 0.2 MPa. With a tensile modulus of 5 MPa, in order forthe implant to strain 2% in conjunction with the degenerated tendon, thestress on the implant will be about 1.0 MPa. With an ultimate tensilestrength of 2 MPa, the strength of the sheet-like structure of theimplant when first implanted will be about two times the expected loads.With a cross-sectional area of 20 mm2, the load on the implant will be20 N. Thus, from a load sharing perspective, the implant will carryabout 20% of the load to experience 2% strain.

Material(s) used in the implanted device should be able to withstand thecompression and shear loads consistent with accepted post surgicalshoulder motions. The perimeter of the device may have differentmechanical properties than the interior of the device, such as forfacilitating better retention of sutures, staples or other fasteningmechanisms. The material(s) may be chosen to be compatible with visual,radiographic, magnetic, ultrasonic, or other common imaging techniques.The material(s) may be capable of absorbing and retaining growth factorswith the possibility of hydrophilic coatings to promote retention ofadditives.

While exemplary embodiments of the present invention have been shown anddescribed, modifications may be made, and it is therefore intended inthe appended claims to cover all such changes and modifications whichfall within the true spirit and scope of the invention.

What is claimed is:
 1. A tendon repair implant for repair of a partialthickness tear of a supraspinatus tendon, the tendon repair implantcomprising: a sheet-like structure having a first compact configurationfor delivery from an arthroscopic instrument and a second planarconfiguration defined by a longitudinal, lateral and thickness dimensionwith a longitudinal surface generally conformable to a bursal sidesurface of the supraspinatus tendon when positioned thereon, wherein thesheet-like structure has a tensile modulus of about 1 MPa to about 100MPa in the range of 1% to 3% strain in the longitudinal dimension and aporosity of about 30% to about 90% with longitudinal pathways defined inthe thickness dimension for at least some tissue in-growth oriented inthe longitudinal dimension.
 2. The implant of claim 1, wherein thesheet-like structure comprises a bioresorbable polymer.
 3. The implantof claim 2, wherein the bioresorbable polymer maintains at least about70% of its tensile strength after 2 months of implantation.
 4. Theimplant of claim 1, wherein upon initial fixation of the sheet-likestructure to the bursal side surface of the supraspinatus tendon, theanatomical load on the tendon and implant combination is distributedwith about 1% to about 50% of the load carried by the sheet-likestructure.
 5. The implant of claim 1, wherein upon initial fixation ofthe sheet-like structure to the bursal side surface of the supraspinatustendon, the anatomical load on the tendon and implant combination isdistributed with about 5% to about 33% of the load carried by thesheet-like structure.
 6. The implant of claim 5, wherein the sheet-likestructure comprises a bioresorbable material having a retention ofstrength of at least about 70% at 2 months after implantation.
 7. Theimplant of claim 1, wherein the longitudinal pathways have a crosssection of about 100 to about 200 microns.
 8. The implant of claim 1,wherein upon fixation to the bursal side tendon surface, cyclic loadingduring rehabilitation facilitates remodeling of tissue in-growth to formtendon-like tissue.
 9. The implant of claim 1, wherein the sheet-likestructure comprises a reconstituted collagen material.
 10. The implantof claim 9, wherein the reconstituted collagen material has preferentiallongitudinal orientation of fibers to form the longitudinal pathways.11. A tendon repair implant for repair of a partial thickness tear of asupraspinatus tendon, the tendon repair implant comprising: a sheet-likestructure having a longitudinal dimension generally parallel to thesupraspinatus tendon when affixed thereto, the sheet-like structurehaving a tensile modulus of about 5 MPa to about 50 MPa in the range of1% to 3% strain in the longitudinal dimension and a porosity of about30% to about 90% with pathways for tissue in-growth running in thelongitudinal dimension within the thickness of the structure.
 12. Theimplant of claim 11, wherein the sheet-like structure comprises areconstituted collagen material.
 13. The implant of claim 12, whereinthe reconstituted collagen material has preferential longitudinalorientation of fibers to form the longitudinal pathways.
 14. The implantof claim 13, wherein the longitudinal pathways have a cross section ofabout 150 to about 200 microns.